| Summary: | This manuscript examines sea ice and snow cover (here defined as “cryo- cover”) across the Northern Hemisphere through a series of three studies. Cryo-cover is unique in that it is both a responder to climate (sensitive to temperature) but is also a climate forcer (via impacting the radiation balance), therefore understanding its complex interactions and how they vary temporally and spatially are imperative for many applications within the atmospheric, environmental, and hydrologic sciences. ☐ The first study builds a climatology of cryo-cover using three datasets: the National Snow and Ice Data Center (NSIDC) Sea Ice Extent (1979 – 2020), the Rutgers Global Snow Lab (GSL) Snow Cover Extent (1979 – 2020), and the MeaSuREs State of the Cryosphere (1979 – 2012) products. Temporal trends of cryo-cover, both as a combined and as separate components are analyzed, and a derived cryo-cover concentration dataset is created using the MeaSuREs values. From these values cryo-cover is classified to be either stable (covered 75% of the time or more, which has decreased in most months over time) or transient (covered less than 75% of the time, which has increased in many months over time). Cryo-cover has predominantly decreased since 1979, with sea ice decreasing in all months and snow cover increasing in some areas in the autumn. ☐ The second study implements the derived cryo-cover concentration dataset (1979 – 2012) to investigate three key transitional cryo-cover months (March, June, and October). Self-Organizing Maps (SOMs) are used to define specific regions of cover transition across the Northern Hemisphere. Results suggest a transition from stable cover to transient cover in March and June as SOM identified stable cover patterns lose spatial area in favor of neighboring patterns with lower average concentration values gaining area over time. October results differ as there were regions experiencing a decrease in stability (especially along the sea ice domain edges) but also regions that experienced increasing ...
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